The Building Code of Australia (BCA) specifies that metal roofing systems must achieve a specific R-Value. This R-Value represents the efficiency of the insulation of the roofing. In particular, Section J of the BCA specifies that thermal insulation of roofing is important for the energy efficiency of the building i.e. the efficiency of the roof insulation is in direct correlation with the amount of energy expended on air conditioning. In order to reduce electricity expenditure, the BCA has outlined what R-Values must be met for certain roof types.
In the case of achieving an R-Value of 3.2, approximately 95-100 mm thickness glass wool building blanket is specified as having the adequate amount of thermal insulation to achieve this value. However, traditional roofing methods squash the roof sheet onto the glass wool and the insulation cannot recover to its full nominal thickness. This means that in practice, with traditional roofing materials commercially available, the R-Value of 3.2 may not be achieved using wool of approximately 95-100 mm thickness.
Attempts have been made to raise the roof sheet above a mounting purlin in order to achieve the maximum R-Value possible, however the applicant has identified that such attempts have created more problems and, specifically, have not solved the problem of fully compressing the wool between the roof sheet and the purlin by using the wool as a packer. Previously proposed systems utilise the height of the compressed wool between the purlin and the raising system to achieve the total height of approximately 95-100 mm.
Compressing the glass wool between the fastening point of the raising system and the purlin creates the following risks:                Vibration and thermal expansion of the roofing arrangement could deteriorate the glass wool between the bracket and the purlin, over time. Compressed glass wool is not a structural material;        Glass wool is not a consistent thickness or density across the one roll, or across manufacturers, the height achieved by using the compressed wool as a raising washer would be inconsistent; and        Compression of the glass wool reduces the R-Value of the system (see FIG. 17).        
The applicant has identified that there is not a commercially available solution on the market which contacts directly to the purlin, will achieve 100 mm height for all roofing profiles and will work in combination with all other commercially available roofing components.
Other problems created by raising the roof sheet include:                Creating the need for the gutter to be raised also;        Reducing the R-Value by compression of the wool atop the purlin; and                    Previously proposed systems cannot be supplemented with an additional component to be cyclone resistant.                        
The applicant has identified that it would be advantageous for there to be provided a product which satisfies the BCA when used in conjunction with currently available roofing products, for any R3.2 roofing situation.
In one existing arrangement for accommodating insulation beneath a roof sheet, the insulation is allowed to sag between the purlins to allow the building blanket to recover to its full nominal thickness (see FIG. 18). However, this arrangement is unsatisfactory as the building blanket is squashed between the roof sheet and the purlin, resulting in a large insulation efficiency loss where the wool is compressed. Also, the amount of sag cannot not be accurately measured, leaving a large margin for error, and the sag decreases the safety factor of the wire mesh beneath the wool. This method has been deemed by some to be less than optimal as it may cause safety risks and may produce poor results.
In another existing arrangement, a raiser bracket is mounted atop compressed glass wool insulation, as shown in FIG. 13. However, with this arrangement the fastening points sit atop the glass wool insulation utilising the compressed wool as a point of height raising, thus also resulting in a large insulation efficiency loss where the wool is compressed. Other disadvantages include that the raiser bracket is unsuitable for corrugated type roofing, and may be 5-10 mm under height if used for this purpose. Furthermore, the bracket must be assembled on site, does not suit the existing clips that roof sheet manufacturers sell with their roof sheeting, and is not rated for cyclonic regions. Also, the raiser bracket is only available in one height, creates problems for re-roofing (it raises the roof line, which in turn means the gutter must be raised to suit), and the length of the design suits the roofing clips, and not the insulation beneath it (insulation building blankets are typically 1200 mm wide).
In summary, the raiser bracket system shown in FIG. 13 involves a method of roofing not compatible with some existing components, and adds the inefficiency of pre-assembly.
Yet another existing arrangement for accommodating insulation beneath a roof sheet makes use of foam spacers. However these may have the following problems:                Utilises the compressed wool beneath it as a point of height raising        Does not attach to the purlin before the roof sheet is fixed. This creates the problem of the spacers sliding on a pitched roof or when the roof sheet is moved.        Long screws without guides are required to fasten the roof sheet to the purlin, this creates the risk of screws not penetrating in a straight line        Foam does not maintain its shape and thickness over time and under pressure as steel does        Compresses the glass wool and detracts from the R-Value        
Existing arrangements may also have the problem of the support platforms being very narrow, making it difficult for roofing workers to balance when walking or kneeling on the brackets/purlins.
Examples of the invention seek to solve, or at least ameliorate, one or more disadvantages of previous roofing systems.